Nested Transactions in PL/pgSQL

Is it possible to nest transactions within a stored procedure?  I have a stored procedure that calls many other stored procedures and what happens it that after a certain amount of time the server runs out of shared memory.  I know I can increase the PostgreSQL shared memory.  However, that would be a temporary fix.  I know it will eventually run out again as more data is processed.  The right way to do it is to do  issue a save point or commit at various places in my long stored procedure.  I want to believe that there is a way to issue commits within a stored procedure since PostgreSQL now supports nested transactions.

Any help or work around would be appreciated.  Thanks.

Andy Nykolyn
Northrop Grumman